Determination of plasma volume by indocyanine green – validation of the method and use in patients after cardiopulmonary bypass

Abstract

Objective: Validation of plasma volume (PV) determination by indocyanine green (ICG) in comparison to the gold-standard method with radioiodinated albumin, and investigation of the effect of commonly used plasma expanders (albumin, hydroxyethyl starch, and polygelatine) on PV in the early postoperative phase in patients undergoing cardiac surgery. Design: Prospective clinical study. Setting: Department of medicine and intensive care unit at a university hospital. Patients and participants: Ten healthy volunteers and 21 patients after elective open-heart surgery. Measurements and results: PV of subjects was measured by i.v. injecting 5 µCi [¹²⁵I]albumin (I-ALB). One hour later, PV was determined by a peripheral i.v. injection of 0.25 mg/kg body weight ICG (ICG1). In five subjects PV was measured repeatedly by ICG (ICG2) 1 h after ICG1. Mean PV of I-ALB and ICG1 or ICG2 showed consistent results. Further, we investigated central vs peripheral intravenous injection of ICG in six patients after open-heart surgery compared to [¹²⁵I]albumin. There was no difference between mean PV measured by [¹²⁵I]albumin and peripheral ICG (P=0.40). PV determined by central injection of ICG was significantly higher than by the other methods. In 15 patients PV was determined by [¹²⁵I]albumin. Thereafter, patients were randomly divided into three groups. Group ALB was infused with 1.75 ml/kg body weight human albumin 20%, group HAES with 5.25 ml/kg body weight hydroxyethyl starch 6%, and group HAEM with 7.0 ml/kg body weight polygelatine 3.5%. PV was measured 1 h and 4 h after infusion by ICG. There were no significant changes in PV between the groups. Conclusions: PV determination by peripheral i.v. injection of ICG produced reliable and consistent results when a reactive hyperaemia was produced by a tourniquet prior to injection. Therefore, central venous injection of ICG may not be prerequisite for precise measurements of PV. The expected acute increase in PV after infusion of commonly used plasma expanders after cardiac surgery was not found.